Drilling fluids or muds are commonly circulated in the well during drilling operations in order to cool and lubricate the drilling apparatus, lift cuttings out of the wellbore and counterbalance the subterranean formation pressure encountered during drilling. An important function of a drilling fluid is to reduce the considerable torque on the rotating drill stem caused by the friction between the outside of the drill pipe comprising the drill stem and the wall of the well and/or casing strings. Drilling through offsets, deep wells and highly deviated or horizontal wells results in increased frictional forces, increasing the demand on the lubricating properties of the drilling fluids.
After drilling a well to the total depth, it is a normal practice to replace the drilling mud with a completion fluid. A completion fluid is typically a solids-free (or acid soluble), non-damaging formulation, which is intended to minimize reductions in permeability of the producing zone. The density of the completion fluid is generally selected and controlled to ensure that the hydrostatic head or pressure of the fluid in the wellbore will match the hydrostatic pressure of the column of drilling fluid being displaced.
The oil and gas industry has used brines for well drilling and well completions for more than thirty years. High density brines have been found to have particular applicability in deep wells, such as those that descend 15,000 to 30,000 feet (4,500 to 10,000 meters). Exemplary of high density brines are sodium chloride, potassium chloride, calcium chloride, sodium bromide, calcium bromide, zinc bromide, potassium formate, cesium formate and sodium formate brines.
While high density brines have been found to be functional in providing the lubricity and viscosity of a well treatment fluid under extreme shear, pressure and temperature variances, they are often ineffective because they are unable to exhibit the constant lubricity which is required during high shear conditions.
During the operation of deep wells, as well as in extended reach and/or high angle wells, it is necessary for the brine-containing well treatment fluid to exhibit increased lubricity. The need for increased lubricity is most marked in those instances during wellbore cleanup, wireline operations, coil tubing operations and during the running of production tubulars.
The literature reports various additives for use as lubricating agents in drilling fluids as well as completion fluids. Many of the reported additives are not, however, compatible with clear brines or drilling fluids or completion fluids which have brine as a major component. In addition, many additives used as lubricating agents in drilling fluids and/or completion fluids today have presented environmental concerns and tend to be costly.
A need exists therefore for lubricating agents which may be used in brine-based drilling fluids and/or completion fluids. Such lubricating agents need to lower torque and drag by reducing metal to metal friction. Furthermore, they need to be useful in the prevention of differential sticking of downhole tubulars. Such lubricating agents further must be environmentally friendly.